Method of producing lattice body for lead storage battery, and lead storage battery

ABSTRACT

A method of producing a grid for a lead-acid battery in accordance with the present invention includes the step of placing lead alloy foil on a base material sheet of a lead-calcium alloy and attaching the lead alloy foil under pressure to the base material sheet. The thickness t of the lead alloy foil, the thickness a of the base material sheet before the attaching, and the thickness b of the composite sheet after the attaching satisfy the relational expression 1.3≦(a+t)/b. The length L of the contact part of rollers with the base material sheet and the lead alloy foil is 10 mm or more. This makes it possible to secure good adhesion of the lead alloy foil to the base material sheet. Also, when this composite sheet is subjected to an expanding process and used as a positive electrode grid, it is possible to provide a lead-acid battery having excellent cycle life characteristics.

TECHNICAL FIELD

The present invention relates to methods of producing grids for use inlead-acid batteries, and more particularly, to methods of producingcomposite sheets used in lead-acid battery grids.

BACKGROUND ART

Lead-acid batteries have conventionally been used in various industrialfields, for example, as car batteries and back-up power sources. Withrespect to lead-acid batteries used in automotive applications, it isrequired to reduce the amount of self-discharge and the amount of lossof water contained in electrolyte (hereinafter referred to as waterloss) for decreasing the number of man-hours needed for repair andmaintenance. To meet such requirements, grids used in positive andnegative electrodes are made of a lead-calcium alloy, which is free fromantimony that increases the amounts of self-discharge and water loss.

Among them, expanded grids obtained by making slits in a rolled sheet ofa lead-calcium alloy and expanding the slits have an advantage of highproductivity. Also, the addition of tin to a lead-calcium alloy provideshigh mechanical strength and corrosion resistance required of lead-acidbattery grids. Thus, expanded grids made of a Pb—Ca—Sn alloy are widelyused.

FIG. 1 shows a production method of a lead-calcium alloy sheet used in aconventional expanded grid. A slab 1, which is a plate-shaped basematerial and obtained by continuous casting of a lead-calcium alloy, isgradually rolled by a plurality of pairs of rollers 2. At this time, thedistance between each pair of rollers in FIG. 1 gradually decreases asthe thickness of the slab 1 decreases. That is, the plurality of pairsof rollers are arranged such that the radius (r_(n+1)) of the n+1_(st)pair of rollers 2 is greater than the radius (r_(n)) of the n_(th) pairof rollers 2. Also, the center distance between adjoining n_(th) pair ofrollers 2 and n+1_(st) pair of rollers 2 is constant. The slab 1 iseventually rolled to a desired thickness, to obtain an alloy sheet 3.

It should be noted that other than the method of FIG. 1, rollers 4 maybe arranged such that the center distance between each pair of rollers 4gradually decreases as the thickness of the slab 1 decreases, while theradius (r) of the rollers 4 is made constant, as illustrated in FIG. 2.

Thereafter, slits are cut in the alloy sheet 3, and the slits areexpanded to obtain an expanded grid having meshes. An active materialpaste is filled into the meshes of the expanded grid, and the resultantgrid is cut to obtain an electrode plate for a lead-acid battery.

As described above, when electrode plates including an expanded gridmade of a lead-calcium alloy are used as positive and negativeelectrodes, there is an advantage that the amounts of self-discharge andwater loss of the resultant lead-acid battery are small, in comparisonwith the cases of including a positive electrode grid made of alead-antimony alloy. However, there is also a drawback of poor cyclelife characteristics in repeating charging and discharging.

As a method for improving the cycle life characteristics, JapaneseLaid-Open Patent Publication No. Sho 61-200670 proposes placing a leadalloy sheet containing one or both of tin and antimony on a basematerial sheet of a lead-calcium alloy, and rolling these two sheets forintegration to obtain a composite sheet. Since tin or antimony containedin the composite sheet has the effect of improving the adhesion of thepositive electrode active material to the positive electrode grid, thecycle life characteristics are improved.

In improving the adhesion of the positive electrode active material tothe positive electrode grid containing tin or antimony, it is importantthat the base material sheet and the lead alloy sheet have goodadhesion. In the next step, the composite sheet is expanded in anexpanding process and therefore undergoes plastic deformation. In thisstep, if the adhesion of the lead alloy sheet to the base material sheetis not good, tiny cracks tend to occur between the base material sheetand the lead alloy sheet. The occurrence of the cracks significantlyimpairs the adhesion of the positive electrode active material to thepositive electrode grid, resulting in a decrease in cycle lifecharacteristics.

As a method for improving the adhesion of the lead alloy sheet to thebase material sheet, Japanese Laid-Open Patent Publication No. Hei5-13084, for example, proposes making the temperature difference betweenthe base material slab and the lead alloy foil attached to this slab150° C. or less. Also, as a method of obtaining such temperaturedifference, there is a proposal of cooling the slab surface with water.

In this way, by regulating the temperature difference between the slaband the lead alloy foil, it is possible to suppress, to some extent, theseparation of the lead alloy foil which occurs when the composite sheetconsisting of the slab and the lead alloy foil is bent. However,completely preventing the occurrence of such separation is stilldifficult. Further, even if the separation of the lead alloy foil is notfound by the visual inspection of the composite sheet, a lead-acidbattery including this composite sheet as the positive electrode gridmay not exhibit expected cycle life characteristics. In this case, it isconsidered that there is such minute separation between the basematerial sheet and the lead alloy sheet that cannot be found by visualinspection.

In view of the above problems, it is therefore an object of the presentinvention to provide a method for producing a lead-acid battery gridformed from a composite sheet, which has excellent adhesion between abase material sheet of a lead-calcium alloy and lead alloy foilcontaining a component effective for improving cycle lifecharacteristics. It is another object to provide a lead-acid batteryhaving good cycle life characteristics by using this composite sheet,which has been subjected to an expanding process, as a positiveelectrode grid.

DISCLOSURE OF INVENTION

A method of producing a grid for a lead-acid battery in accordance withthe present invention includes the steps of: (1) passing lead alloy foiltogether with a base material sheet of a lead-calcium alloy between apair of rollers to attach the lead metal foil to the base materialsheet, to make a composite sheet, and (2) passing the composite sheetbetween a plurality of pairs of rollers to gradually roll the compositesheet to a predetermined thickness. The thickness t of the lead alloyfoil, the thickness a of the base material sheet, and the thickness b ofthe composite sheet in the step (1) satisfy the relational expression:1.3≦(a+t)/b. The length of the contact part of the rollers of the step(1) with the base material sheet and the lead alloy foil is 10 mm ormore in the longitudinal direction of the base material sheet.

It is preferable that the temperature difference between the basematerial sheet and the lead alloy foil be 50° C. or less in the step(1).

It is preferable that the lead alloy foil includes a lead alloycontaining at least one selected from the group consisting of Sn, Sb andAg.

It is preferable that the method further includes the step (3) ofsubjecting the composite sheet to an expanding process after the step(2).

Also, the present invention relates to a lead-acid battery using alead-acid battery grid obtained by the above-described production methodas at least a positive electrode grid.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a drawing showing a conventional process of rolling a slab.

FIG. 2 is a drawing showing another conventional process of rolling aslab.

FIG. 3 is a drawing showing a production process of a composite sheet inaccordance with a method of producing a grid for a lead-acid battery ofthe present invention.

FIG. 4 is a drawing showing the main part of the production process of acomposite sheet in accordance with the method of producing a grid for alead-acid battery of the present invention.

FIG. 5 is a drawing showing a process of obtaining an electrode platefrom the composite sheet.

FIG. 6 is a perspective view, partially cut away, of a lead-acid batteryin accordance with the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Referring now to FIG. 3, embodiments of the present invention aredescribed. FIG. 3 shows a production process of a composite sheet inaccordance with a method of producing a grid for a lead-acid battery ofthe present invention.

In a rolling process of a lead alloy sheet used in a grid, six pairs ofrollers 12 are provided. These pairs of rollers have the same size(radius) and are arranged such that the center distance between eachpair of rollers decreases as the thickness of a base material sheetdecreases. Also, the rollers in each pair are arranged such that thecenter distance between adjacent pairs of rollers is equal in thelongitudinal direction of the base material sheet.

First, a slab 11 of a lead-calcium alloy is passed, as a base materialsheet, between the first pair of rollers 12 a. The slab 11 is obtained,for example, by a method of continuously casting a molten lead alloycontaining a predetermined concentration of calcium, or by a method ofpulling out this molten lead alloy from the slit which has apredetermined size and is formed in the tip end of a nozzle. Thethickness of the slab 11 is generally around 10 to 20 mm.

In order to secure the mechanical strength of the base material sheetand the lead-acid battery grid formed from this sheet, the base materialsheet is preferably a lead alloy containing 0.03 to 0.10% by mass ofcalcium.

Further, in order to secure the corrosion resistance as well as themechanical strength of the lead-acid battery grid formed from the basematerial sheet, the base material sheet is preferably made of a Pb—Ca—Snalloy. Also, the Pb—Ca—Sn alloy preferably contains 0.03 to 0.10% bymass of Ca and 0.80 to 1.80% by mass of Sn.

It should be noted that the lead alloy of the base material sheet issubstantially free from antimony, for the purpose of reducing theamounts of water loss and self-discharge. However, the lead alloy maycontain, as an impurity, about 0.001 to 0.002% by mass of antimony,which is an amount that will not have a bad effect on the amounts ofwater loss and self-discharge. Further, the lead alloy may contain, asan impurity, about 0.001 to 0.01% by mass of bismuth, about 0.005 to0.02% by mass of aluminum, or about 0.001 to 0.08% by mass of barium,which is an amount that will not have a bad effect on the batterycharacteristics.

Next, lead alloy foil 14 is placed on the surface of the slab 11 beforethe slab 11 is fed between the second pair of rollers 12 b, and the leadalloy foil 14 and the slab 11 are fed together between the second pairof rollers 12 b. Then, the slab 11 and the lead alloy foil 14 aresimultaneously rolled by the rollers 12 b, so that the lead foil 14 isattached under pressure to the slab 11 and a composite sheet is obtained(step (1)). For example, the obtained composite sheet may be subjectedto an expanding process to form a grid, as described above.

The lead alloy foil 14 is preferably made of a lead alloy containing atleast one selected from the group consisting of Sn, Sb and Ag. Morepreferably, the lead alloy 14 is made of a lead alloy containing atleast one selected from the group consisting of 1 to 10% by mass of Sn,1 to 10% by mass of Sb, and 0.05 to 1.0% by mass of Ag. When a compositesheet including the lead alloy foil 14 of such composition is used as apositive electrode grid, the cycle life characteristics of the resultantlead-acid battery are improved. The thickness t of the lead alloy foil14 is preferably about 0.05 to 0.30 mm.

Also, when the lead alloy foil 14 is attached under pressure to the slab11, the temperature difference between them is preferably 50 or less.This further improves the adhesion of the lead alloy foil 14 to the slab11. This temperature difference is controlled, for example, by makingthe temperature of the lead alloy foil the same as room temperature andadjusting the temperature of the slab, obtained by continuous casting,by water cooling.

Also, the rollers are heated by the heat generated by the rolling of theslab. If the temperature of the rollers increases excessively, leadadheres to the surfaces of the rollers, impairing the smoothness of theslab surface. To address this problem, for example, the temperature ofthe surfaces of the rollers can be controlled at about 80 to 90° C. by amethod of spraying a dispersion of rust-inhibiting oil on the rollers.

FIG. 4 is an enlarged drawing of a part of FIG. 3, at which the leadalloy foil 14 is attached to the slab 11. At the second rollers to whichthe lead alloy foil 14 is fed, the thickness a of the slab 11immediately before the rolling, the thickness b of the composite sheetimmediately after the rolling, and the thickness t of the lead alloyfoil 14 satisfy the following expression (1):1.3≦(a+t)/b  (1)

Further, a contact part 15 of each of the rollers 12 b with the leadalloy foil 14 placed on the slab 11 has a length L of 10.0 mm or more inthe longitudinal direction of the slab.

The length L is given by the expression (2), using the radius r of thereduction roller 12 b and the angle θ (radian), which a straight linex-z forms with a straight line y-z at the central axis z of thereduction roller 12 b, when the opposite ends of the contact part 15 arerepresent by x and y respectively.L=θr  (2)

Also, the radius r is given by the following expression (3), using thethickness a of the slab, the thickness b of the composite sheet, thethickness t of the lead alloy foil, and the angle θ.r={(a+t)/2}−(b/2)}+rcos θ  (3)And, θ is given by the following expression (4) by modifying theexpression (3).θ=cos⁻¹[1−{(a+t−b)/2r}]  (4)

Accordingly, from the expressions (2) and (3), the length (L) is givenby the following expression (5).L=r·cos⁻¹[1−{(a+t−b)/2r}]  (5)

That is, r, a, t and b satisfying the length L of 10.0 mm or more, andthe above expressions (1) and (5) may be determined.

Thereafter, the composite sheet is gradually rolled by the third andsubsequent pairs of rollers 12 (12 c, 12 d, 12 e, and 12 f), and acomposite sheet 13 having a desired thickness is obtained (step (2)).The thickness of the rolled composite sheet 13 may be determinedaccording to the battery design, but it is generally about 0.5 to 1.5mm.

The composite sheet obtained by the above method has good adhesion, andthe occurrence of separation of the lead alloy foil 14 from the slab 11is suppressed.

Further, when the rolled composite sheet 13 is subjected to an expandingprocess and used as a positive electrode grid, it is possible to obtaina lead-acid battery of the present invention in the conventional manner.In the lead-acid battery of the present invention, the lead alloy layer,containing antimony, tin, or silver and formed on the surface of thepositive electrode grid, adheres firmly to the base material layer.Therefore, the positive electrode active material and the positiveelectrode grid have good adhesion, so that the cycle lifecharacteristics can be significantly improved.

Although this embodiment has described a process of feeding lead alloyfoil to the second pair of six pairs of rollers, the number of pairs ofrollers and the pair of rollers to which the lead alloy foil is fed arenot particularly limited to these.

In the following, examples of the present invention are described indetail.

EXAMPLE

(1) Production of Positive Electrode Plate

First, a composite sheet was produced by the same procedure as thatexplained with reference to FIG. 3.

A slab 11, which was obtained by continuous casting of a molten Pb—Ca—Snalloy containing 0.07% by mass of Ca and 1.2% by mass of Sn, was used asa base material sheet. The thickness a of the slab 11 before the rollingby rollers 12 b was 11.0 mm. A Pb—Sn—Sb alloy containing 5.0% by mass ofSn and 5.0% by mass of Sb was used as lead alloy foil 14. The thicknesst of the lead alloy foil 14 before the rolling was 0.20 mm. Thethickness of a composite sheet 13 obtained as the result of this rollingprocess was 1.1 mm.

Subsequently, predetermined slits were cut in the rolled composite sheet13, and then, the slits were expanded to form meshes 5 ((a) of FIG. 5),so as to obtain an expanded grid (expanding process). It should be notedthat this expanding process was not applied to the central part of thecomposite sheet 13, since a tab 7 a, given below, is formed on thispart. A positive electrode paste 6 was filled into the meshes 5 ((b) ofFIG. 5), and the resultant grid was cut into the form of an electrodeplate having the tab 7 a ((c) of FIG. 5), so as to obtain an electrodeplate 7. Thereafter, the electrode plate 7 was cured and dried, so as toobtain an unformed positive electrode plate 21.

The positive electrode paste used was prepared by adding water andsulfuric acid to a lead powder including 10 to 30% by mass of lead oxideand 90 to 70% by mass of metallic lead and kneading the mixture.

(2) Production of Negative Electrode Plate

A slab, obtained by continuous casting of a molten Pb—Ca alloycontaining 0.07% by mass of Ca, was rolled to obtain a rolled sheet.Then, in the same manner as the positive electrode plate, the rolledsheet was subjected to an expanding process, filled with a negativeelectrode paste, and cut into the form of an electrode plate, so as toobtain an electrode plate. Thereafter, the electrode plate was cured anddried to obtain an unformed negative electrode plate 22.

The negative electrode paste used was prepared by adding water andsulfuric acid to a lead powder including 10 to 30% by mass of lead oxideand 90 to 70% by mass of metallic lead and kneading the mixture.

(3) Fabrication of Lead-Acid Battery

A lead-acid battery having the structure as illustrated in FIG. 6 wasproduced by the following manner. FIG. 6 is a perspective view,partially cut away, of the lead-acid battery.

The positive electrode plates 21 and the negative electrode plates 22obtained in the above manner were stacked with separators 23 interposedtherebetween. Straps 24 and 25 were formed by welding together the tabsof the electrode plates of the same polarity, so as to obtain a platepack 28. The plate pack 28 was accommodated in each of a plurality ofcell compartments 31 divided by partitions 30 of a container 29, andadjoining plate packs 28 were connected in series by a connector 27adjacent to and connected to the strap 24. In this example, theconnection between the electrode groups was made via a through-hole (notshown) formed in the partition 30.

With respect to the plate packs 28 located at opposite ends of theseries connection, one of them was provided with a positive pole (notshown), and the other was provided with a negative pole 26. While acover 32 was fitted to the opening of the container 29, a positiveelectrode terminal 33 and a negative electrode terminal 34 of the cover32 were welded to the positive pole and the negative pole 26.Thereafter, dilute sulfuric acid was injected into the cell compartmentsfrom the liquid inlets formed in the cover 32, to perform charging.After the charging, a vent cap 35 was fitted to each liquid inlet, toproduce a lead-acid battery for starting (hereinafter referred to asbattery) of 55D23 defined by JIS D 5301.

The length L of the contact part of the reduction roller with the basematerial sheet and the lead alloy foil, as well as the value of (a+t)/b,were varied, as shown in Table 1, by changing the center distancebetween the second pair of rollers 12 b and the radius r thereof in theabove-described production process of the composite sheet. Also, thetemperature difference between the slab and the lead alloy foil wasvaried, as shown in Table 1, by keeping the temperature of the leadalloy foil 20′ and adjusting the temperature of the slab by watercooling.

It should be noted that the radius r of the rollers 12 a and 12 c to 12f, excluding the second pair of the process as illustrated in FIG. 4,was 85 mm. The center distance between the first pair of rollers wasmade 180.4 mm, and the center distance between the third to sixth pairsof rollers 12 c to 12 f was determined such that the amount of thickreduction by the rolling become constant. In Table 1, batteries 5, 6, 8,10, 12 to 15, 17, and 18 are Examples of the present invention, andbatteries 1 to 4, 7, 9, 11, and 16 are Comparative Examples. TABLE 1Temperature Battery Length L difference No. (a + t)/b (mm) (° C.) Lifecycle Battery 1 1.20 8 20 105 Battery 2 1.20 10 20 105 Battery 3 1.20 2020 110 Battery 4 1.30 8 20 100 Battery 5 1.30 10 20 140 Battery 6 1.3020 20 145 Battery 7 1.30 8 50 90 Battery 8 1.30 10 50 140 Battery 9 1.308 60 80 Battery 10 1.30 10 60 130 Battery 11 1.60 8 20 90 Battery 121.60 10 20 150 Battery 13 1.60 10 50 150 Battery 14 1.60 10 60 135Battery 15 1.60 20 20 150 Battery 16 2.00 8 20 80 Battery 17 2.00 10 20135 Battery 18 2.00 20 20 140[Evaluation of Cycle Life Characteristics]

Batteries 1 to 18 listed in Table 1 were subjected to a low load lifetest (JIS D5301) under the following conditions.

The batteries were charged at a maximum current of 25 A and a constantvoltage of 14.8 V for 10 minutes, and then discharged at a constantcurrent of 25 A for 4 minutes. This cycle was repeated. Every 480 cyclesof such charging and discharging, the batteries were discharged at aconstant current of 356 A for 30 seconds. When the discharge voltage atthe 30th second lowered to 7.2 V, the batteries were judged as havingreached the end of their life.

These results are shown in Table 1. The cycle life in Table 1 is anindex obtained by defining the cycle number at which the battery 4reached the end of its life as 100.

As a result, it was found that the batteries of Examples had bettercycle life characteristics than the batteries of Comparative Examples.Also, when the temperature difference between the slab and the leadalloy foil was 20 to 60° C., excellent cycle life characteristics wereobtained. However, when the temperature difference was 60° C., the cyclelife characteristics were slightly lower than when the difference was20° C. and 50° C. It is therefore preferable that the temperaturedifference be 50° C. or less.

Next, the respective batteries were decomposed and examined after thelife tests. The batteries of Examples exhibited remarkable softening ofthe positive electrode active material, and it was found that thesebatteries reached the end of their life because of the deterioration ofthe active material itself. On the other hand, with the batteries ofComparative Examples, partial separation of the lead alloy foil from thepositive electrode grid was observed. Also, a large amount of positiveelectrode active material shed from the positive electrode grid,although the softening of the positive electrode active material was notso remarkable in comparison with the batteries of Examples.

From these results, it is considered that the batteries of ComparativeExamples reached the end of their life because the minute separation ofthe lead alloy foil from the positive electrode grid caused a decreasein the interfacial adhesion of the positive electrode active material tothe positive electrode grid. By contrast, according to the presentinvention, it is thought that the cycle life characteristics weresignificantly improved because the positive electrode active materialand the positive electrode grid had good interfacial adhesion.

In this example, an expanded grid was used as the negative electrodegrid, but the same effects as described above can be obtained by using acasting grid, which is obtained by injecting a molten lead into a moldand solidifying it.

INDUSTRIAL APPLICABILITY

As described above, in a production process of a composite sheet inwhich lead alloy foil, which is effective for improving cycle lifecharacteristics, is attached under pressure to a base material sheet ofa lead-calcium alloy, the present invention can provide a method ofproducing a grid for a lead-acid battery, by which good adhesion of thelead alloy foil to the base material sheet is secured. When thiscomposite sheet is subjected to an expanding process and used as apositive electrode grid, it is possible to provide a lead-acid batteryhaving good cycle life characteristics.

1. A method of producing a grid for a lead-acid battery, comprising thesteps of: (1) passing lead alloy foil together with a base materialsheet of a lead-calcium alloy between a pair of rollers to attach thelead alloy foil to the base material sheet, to make a composite sheet,and (2) passing the composite sheet between a plurality of pairs ofrollers to gradually roll said composite sheet to a predeterminedthickness, wherein the thickness t of the lead alloy foil, the thicknessa of the base material sheet, and the thickness b of the composite sheetin said step (1) satisfy the relational expression:1.3≦(a+t)/b, and the length of the contact part of the rollers of saidstep (1) with the base material sheet and the lead alloy foil is 10 mmor more in the longitudinal direction of the base material sheet.
 2. Themethod of producing a grid for a lead-acid battery in accordance withclaim 1, wherein the temperature difference between the base materialsheet and the lead alloy foil is 50° C. or less in said step (1).
 3. Themethod of producing a grid for a lead-acid battery in accordance withclaim 1 or 2, wherein the lead alloy foil comprises a lead alloycontaining at least one selected from the group consisting of Sn, Sb andAg.
 4. The method of producing a grid for a lead-acid battery inaccordance with claim 1, further comprising the step (3) of subjectingthe composite sheet to an expanding process after said step (2).
 5. Alead-acid battery using a lead-acid battery grid obtained by theproduction method of claim 4 as at least a positive electrode grid.